# Logisim libraries

Every Logisim project is automatically a library that can be loaded into other Logisim projects: Just save it into a file and then load the library within another project with the menu | Project |→| Load Library |→| logisim-evolution library... |. All of the circuits defined in the first project will then be available as subcircuits for the second. This feature allows you to reuse common components across projects and to share favorite components with your friends (or students).
Below our project loaded as a library is available in the navigation panel.

Note: The library must not contain a circuit with the same name as a circuit already present in the project.

Each project has a designated main circuit, which can be changed to refer to the current circuit via the menu | Project |→| Set As Main Circuit |. The only significance of this is that the main circuit is the one that is displayed when you first open the project. The default name ("main") of the circuit in a newly created file has no significance at all, and you can feel free to delete or rename that circuit.

With a loaded Logisim library, you are allowed to view circuits and manipulate their states, but Logisim will prevent you from altering the circuits' design and other data stored within the file.

If you want to alter a circuit in a loaded Logisim library, then you need to open it separately within Logisim. As soon as you save it, the other project should automatically load the modified version immediately; but if it does not, you can right-click the library folder in the explorer pane and select | Reload Library |.

Next: User's Guide.